Apparatus for the manufacture of smokeless powder



Feb. 27, 1945. B TROXLER 2,370,271

APPARATUS FOR THE MANUFACTURE OF SMQKELESS POWDER Filed Feb. 2, 1943 HEATER CONDENSER HEATER 25 SCREEN Ber-nharf Trox/er' INVENTOR www ATTORNEY QESPRINKLER FEED Patented Feb. 27,1945

APPARATUS FOR THE MANUFACTURE OF SMOKELESS POWDER Bernhart Troxler, Kenvil, N. J., asslgnor to Hercules Powder Company, Wilmington, Del., a.

corporation of Delaware Application February 2, 1943, Serial No. 474,442

2 Claims.

This invention relates to an improved apparatus for manufacturing propellent smokeless powder and more particularly to an improved apparatus for recovering the excess solvent from, and the drying of, single base smokeless powder.

It is well known by the art that smokeless powder manufacture includes the following steps: The dehydration of the raw material; nitrocellulose or reclaimed smokeless powder; the colloiding of the dehydrated material with a solvent or solvents, for example, an ethyl ether-ethyl alcohol or an acetone-ethyl alcohol mixture; the forming of the colloided mass into strands by pressing through one or more dies; the cutting of these strands into short lengths called grains; the treating of the grains to remove the excess solvent; the drying of the treated grains; the screening of the grains to remove clusters and foreign material and the blending of the dry grains to produce a uniform product.

In the above process the steps of dehydration, colloiding, pressing, cutting, and blending have been developed to a high state of efficiency and comparative safety but the step of processing the grains to remove the excess solvent, the step of drying the grains; and the step of screening of the grains, at present, from a standpoint of efficiency, economy, and safety show many disadvantages.

Now in order to produce a. smokeless powder that will give satisfactory ballistics, it is necessary to control the amount of total volatile matter, retained in the grains, within very definite limits. Such limits are determined by the type of powder and the ballistics required. Therefore, the removal of the excess solvent and moisture from the grains is of the utmost importance in the manufacture of an acceptable powder. These two steps also have an economic effect on the process as the time required and the equipment needed for recovering the excess solvent and for the drying of the powder have a very definite bearing on the per pound cost of the completed powder.

The art originally placed the powder grains in small batches in a dry house after the cutting operation and by forcing air through the mass drove the solvents from the grains. It is obvious that this was a very expensive operation as the solvents were lost. At present, the method of removing and recovering the solvents from the grains includes placing the powder grains in a solvent recovery system that consists of a number of rectangular boxes or bins that have airtight covers and are equipped with means of circulating heated air through the mass of grains and past condensing coils that remove the solvent vapors picked up by the air upon passage through the powder. The system provides for the continuous circulation of the air with alter nate heating, pick up of vapors, and the removal of vapors and this process of circulation is continued until the solvent content of the grains is reduced to a low per cent. There are means provided in the system to remove all condensed vapors to a storage tank where they await recovery by rectification. The reduction of the solvent content-of the powder grains by this method cannot be carried out to the desired low pertotal volatile content desired. The dry-houses I are expensive and the drying procedure is hazardous. The powder is loaded in wooden trays that are positioned in the dry-house to allow air circulation which must be controlled in regard to temperature and speed, as high temperatures cause excessive deterioration and the pos sibility of fire, while excessively fast drying caused by rapid circulation causes uneven drying.

From the dry-houses the powder must be placed in storage or taken direct to a screen house to remove all clusters and foreign material. From the screening operation the powder is stored or taken directly to the blender where a substantially uniform product is produced.

It will be apparent to those skilled in the art that each of the described processes requires at least two handlings of the powder and further that each time powder is handled there are losses and the operators are exposed to the inherent hazard of handling explosives. It is also well accepted that excessive handling of material and the use of batch processes are very expensive and undesirable.

Efforts to perform the same operations in one or more vessels of large capacity have not been attended with any degree of success. When a mass of solvent-wet smokeless powder grains is loaded into a vessel of large capacity for solvent recovery or water drying of the grains, at least two factors must be coped with. The weight of the last portions of the charge added to the vessel presses down on the lowermost portions of the mass and tends to form agglomerates or clusters of grains which resist the desired drying and solvent removal steps. Of equal, if not greater, importance is the formation of individual grains which depart from the uniform grain shape and size; i. e., distortion of the grains. This may occur as part of or apart from clustering or agglomeration of a plurality of grains. These clusters have to be screened out and reprocessed. Furthermore, there is a distinct tendency for the mass of the powder rains to present non-uniform resistance to the treating This, results in non-uniform drying and channeling of the drying fluids through the mass at points of least resistance. This, in turn, may and frequently does cause the same distortion of individual grains and the same clustering or agglomeration which may also result from the mere superimposed weight of the mass of grains on the lower portions of the mass. Since it is the goal of the smokeless powder manufacturers to produce ammunition, every grain of which is uniform in siz and chemical constitution, any treatment which forms non-uniform grains, or causes distortion, is a departure from that goal.

It is the object of this invention to provide an improved apparatus for the solvent recovery and drying of colloided smokeless powder. It is the particular object of the invention to provide a method of recovering solvent from solvent-wet smokeless powder in large batches without causing appreciable distortion, clustering or agglomeration of the individual grains. It is also an object of the invention to provide an apparatus for carrying out the solvent recovery step, the waterdry treatment and the air drying of smokeless powder in large bulk without the necessity for handling the powder between each of these operations. Another object is to provide an apparatus for removing the solvent from smokeless powder in large volume economically, rapidly and safely to provide smokeless powder having uniform ballistic properties.

It has now been discovered, in accordance with this invention, that smokeless powder grains resulting from colloiding a mixture comprising nitrocellulose with a solvent, pressing the colloided nitrocellulose into strands and cutting the nitrocellulose strands into grains of smokeless powder of any desired size, may be uniformly processed in large bulk to produce uniform grains without distortion, clustering and agglomeration by performing certain procedural steps in the apparatus described. Ithas been found that it is essential, at least in the solvent recovery stage of the process, to dispose a mass of solvent-wet smokeless powder grains in a body which presents uniform resistance throughout the body to the passage of the treating fluid therethrough. Wh r such uniform fluid resistance is achieved, there is a substantial absence of channelling and the formation of clusters or agglomerates. The improved apparatus of this invention makes it possible to perform the above operations in the described manner with a high degree of efficiency. More particularly, the improved apparatus facilitates the operation of disposing the large bulk of powder grains in a body which presents uniform resistance throughout to passage of treating fluid therethrough. The process for the solvent recovery and drying of smokeless powder utilizing the described apparatus is set forth more specifically and claimed in my copendin application, Serial No. 474,443, filed on February 2, 1943.

To facilitate an understanding of the improved apparatus of this invention, a detailed description of the apparatus shown in the single figure of the drawing will be made.

The tank I, which is shown in section, is of a novel design that permits the carrying out of the solvent recovery, water-dry, and air-dry process steps without disturbing the powder charge once it has been placed in the tank. The tank I, preferably of relatively large size such as to hold several thousand pounds of powder, has an opening 2 at the top which is closed by a cover 3 that is shaped to fit into the water seal trough 4 around the opening 2. The cover 3 is further designed in the shape of a funnel preferably having a slope of about 40 and the funnel has an opening 5 located directly above the center of the tank I. The opening 5 is closed by suitable means, not shown, such as with a rubber or wooden plug. Directly under the center of the opening 5 in the cover 3 is the top point 6 of a conical spreader l, which may be made in two sections 8 and 9. Section 8 is made removable in order to allow inspection of the inside of the tank while section 9 is stationary and extends to within about six inches of the side of the tank and thus causes the even distribution of the powder within the tank and toward the inner periphery of the wall of the tank. The slope of the conical spreader preferably has a slope of about 35. This peripheral loading may be accomplished by providing an annular opening instead of the spreader but the spreader is most convenient in operation.

The tank I also has a false bottom or support I 0 which is shaped like an inverted cone. This support provides for the removal of the powder charge through valve I2 centrally located in the bottom of the tank and concentric with the axis of the cone. The cone-shaped false bottom preferably is of smooth metal which is perforated or of screen material rolled to provide a smooth surface. The openings in the plate or screen are of a size which prevents the powder grains from passing through but which will allow the free circulation of a fluid medium throughout the tank. It will be understood that the perforations or the mesh may be altered to suit the type of powder being processed. The cone-shaped bottom is designed so that the angle or slope is preferably about 30 and is between about 25 and about 33". This angle of slope is important as it corresponds closely to the angle of repose of powder grains and, therefore, provides a mas of powder which has a uniform thickness and a uniform resistance to the passage of fluid media that may be used to remove solvent to dry the powder grains. I have found that it is preferable that the supporting bottom or screen be inclined at an angle of between about 28 and 30 although angles between about 25 and about 33 operate successfully. Any major departure between this range of inclination will cause the mass of powder dropped onto the inclined surface to build up in a non-uniform body which will influence the reslstance of the mass to fluids passing therethrough and make the resistance non-uniform.

I prefer that the cone-shaped support I0 be fabricated from a material which will not spark. For this purpose, copper, aluminum or plastics may be employed. I also prefer that the support or bottom have as many small openings as possible in order to facilitate uniform passage of the fluid through the support and through the supported body of powder grains. I have found that if the holes are about .025 inches to about .050 inches in width, the desired purpose will be accomplished satisfactorily. Plates having openings or screens having a mesh within this preferred range will satisfactorily support powder grains which are from about 0.2 to about 0.5 inch in diameter and from about 0.5 to about 2.0 inches in length. My greatest preference is for a bottom or support fabricated from a perforated plate but the support may, if desired, be fabricated from screen of the desired mesh if the screen be rolled to give it a smooth surface.

The valve I2 in the bottom of the tank may be of any type suitable for removing the powder grains from the tank. The type shown consists of a plunger I4 attached to a rod I5, acting through a guide I6, that extends to within a few inches of top point 6 of the spreader I. The valve I2 is, therefore, easily operated, from the top of the tank. A slot type valve has also been found suitable but the valve used should obviously be one which will not tend to jam the powder grains when operated and, further, the valve must be water and vapor tight. The valve shown is designed to prevent powder from filling the actual center of the tank. This enlarged valve stem insures th passage of gases through the mass of powder since there are no powder grains directly above the valve face. The discharge gate I3 under valve I2 may be used to control the rate of emptying the powder grains from the tank. It may be of conventional design.

The tank should be of vaporproof and waterproof design and may be fabricated from aluminum, copper, or the like, or may be a lined wooden tank. While ferrous alloys may be used, it is not desirable to include any metal from which sparks may be struck due to the explosive nature of the powder charge. Further, the tank is equipped with the necessary air and water valves to carry out the processes and the method of making such connections will b obvious to those skilled in the art.

There now follows a description of the process for treating the powder in the described apparatus of this invention. The grains of powder from the cutting machine may be processed, in the single tank I described hereinbefore, to the point where they are ready for screening prior to blending, or they may be placed in th tank for any single step or combination of the steps of solvent removal, water drying, air drying, cooling and screening. The process with reference to the figure is carried out by loading tank I, via opening 5, with powder grains from the cutting machines. The spreader distributes the powder evenly within the tank I and also aids in breaking up any clusters of powder that may have formed while the powder grains were in the container at th cutting machine.

The tank I is preferably filled with powder to about the bottom of the spreader 1 by a slow or incremential loading procedure into the tank while maintaining a heated, gaseous medium therein, the loading of the tank being carried out in such a manner as to establish in the tank a bed of smokeless powder grains which has both its upper and lower surfaces close to, if not identical with, the angle of repose of the grains in the mass. The loading of the powder grains in th manner described just above while simultaneously subjecting the grains to solvent removal fluids, particularly a heated non-reactive gas, achieves preliminary and progressive hardening of the grains to prevent distortion and clustering. Durlug such slow or intermittent charging of the tank, the three-way 'valve I1 is set to allow the circulation of a heated gaseous medium, air, or an inert gas, preferably exhaust gases, from fan ll through heater I 8 down through the owder in tank I, out through the three-way air valv I! to the condenser 20. The hot gas from the heater I0 absorbs solvent vapor from the powder and substantially all these absorbed vapors are re moved by the condenser 20 after which the air is recirculated through the system to pick up more solvent vapors. There are means provided in the system to removeall condensed vapors to a storage tank where they await recovery by rectification. The circulation may be intermittent during the charging of the tank I, for example, the fan I8 is cut off while powder is being dump d into the tank but when the tank is filled to the desired height the circulation of air is continuous until the solvent content is reduced to a low percentage. If the tank is filled above the edges of the spreader, the top section 8 thereof may be removed to aid circulation. The powder grains loaded into the tank normally are brought to the tank from the cutting machines in containers, i. e., roving cans, holding about 50-100 pounds of powder grains. The speed with which the tank is filled depends entirely upon the rate of cutting powder, and this filling operation thus may be an intermittent process that may require only a few hours or may extend over a period of two days or even longer.

After removal of the solvent by uniform gas circulation th residual solvent is removed and this is accomplished by closing the three-way air valve I1 and adjusting the three-way water valve 2| to allow the tank I to be filled with hot water or other inert liquid. The tank I is filled to an overflow pipe 22 above the level of the powder, and the valve ZI then so adjusted to keep sufiicient water circulating to maintain the proper temperature. During the water-dry operation, the cover 3 is removed to allow all vapors to escape to the air. This water-dry operation is continued until the residual solvent is removed from the grains to a point that complies with the particular specification being used, after which the powder is ready to be air-dried.

The air-drying of the powder may be accomplished by draining the water from the tank I through valve 2I and then so adjusting valve I! that hot gases from the fan 23 may be blown through heater 24 into tank I and through the powder. Th hot gas uniformly dries the powder because the resistance of the powder mass is substantially equal due to the loading of the powder upon the false bottom sloped at the angle of repose of the powder. The cover 3 is left open and the drying air is exhausted to the atmosphere.

The powder at the end of the drying operation the proper moisture content and is, of cour quite hot. To prevent the handling of hot powder, the heater 24 is turned off and cold gases blown through the powder until the powder temperature is approximately equal to room temperature.

The powder is now ready to be removed from the tank and this is accomplished by opening the valve I2 in the bottom of tank I and allowing the powder to run freely from the tank. The coneshaped false bottom I 0 which has an angle of slope substantially equal to the angle of repose of the powder and has a smooth surface aids the dumping of the tank as will be apparent from the drawing. A screen may be located iust below the valve whereby the powder is screened as the tank is emptied and the valve I! may be so regulated that the amount of powder leaving the tank I may be conveniently screened and packed into bags. The powder after being bagged is ready to be sent to the blender or to storage and the tank I from which it was removed is ready for another charge of powder.

The heaters l9 and I4 may be fed with steam and may be automatically regulated to maintain the desired gas temperatures during the solvent recovery and air-drying operations. The fans II and 23 should be of suflicient capacity to efllciently remove the solvents and water from the powder in the desired lengths of time. It will be obvious that the fan 23 for drying the powder will be of much greater capacity than the fan l8 used to circulate air for removing the solvent vapors.

The three-way valves l1 and 2| may be standard air and water valves or a series of connections may be made to perform the function of these two valves.

The screen is positioned under the dumping valve 12 and is designed and placed to obtain effective screening of whatever type of powder is being manufactured. It is desirable to have a screen holder that allows changing of screens easily if a variety of granulations are to be manufactured. The screen, as will be obvious may be equipped to remove large and small particles of powder and may also be equipped-with any suitable means for aiding in bagging the powder. A screen used in screening powder is preferably not of the vibrating type and, therefore, the screen used in this invention has been placed at an angle and the powder allowed to flow over it by gravity.

In the specific description given hereabove, using the described apparatus, the solvent recovery, water-dry and air-dry steps have been described as being carried out successively in the same vessel, the air-dry powder being discharged onto a suitable screen and then packaged for storage or shipment. This, as has been stated above, is a virtue of my preferred type of apparatus, namely, that the apparatus permits these three steps to be carried out successively without handling and without removal from the vessel until the air-drying of the powder has been achieved. The combining of the four operations of solvent recovery, water-dry, air-dry and screening in one tank and particularly the first three of these, has made it possible to eliminate practically all handling of the powder between the individual steps. Also, since each of these operations has usually been carried out in a special building, it has become possible as a result of the described process to eliminate threequarters of the buildings and equipment needed to process the powder.

In the operation of the apparatus of this invention, it has been found that air or various inert gaseous mediums such as CO2, N2, He, flue gases, or exhaust gases may be circulated through the powder charge to remove the excess solvent and it has been found desirable to use a gaseous medium which will not support combustion and preferably exhaust gases from internal combustion engines are used. A temperature up to about 75 C. may be used but a temperature within the range of about 50 C. to about 60 C. has been found most preferable. The so-called water-dry step is preferably carried out by treating the powder charge with water at a temperature which may be as high as 75 C. but it is preferable to operate within the range of about 50 C. to about 60 C. Any liquid which is not a solvent for any of the ingredients of the powder being treated may be used. After the water-dry step, the liquid remaining is preferably removed by exhaust gases at a temperature as high as 75 C. but a temperature of about 50 C. to about 60 C. is preferable. Any inert gas or air may be used to remove the liquid remaining in the powder from the waterdry treatment.

It has been found that the removal of solvent from grains disposed in the tank shown is much more eillcient than any of the known prior art means. The solvent content of the grains is reduced to the desired percentage quicker and with no distortion, clustering or agglomeration. The excellent solvent removal may possibly be attributed to the method of loading and to the disposing of the grains in a mass having substantially equal gaseous resistance. Further, the removal of solvent during loading to harden the grains is most advantageous as all clustering and distortion is prevented. V

In addition to the elimination of many of the dangerous handlings and transferals from one apparatus to another, required by the prior art, my invention introduces other safety' factors. In the prior art dry-house operation, large amounts (as high as 50,000 to 100,000 pounds) of dry powder were frequently processed for many days in a single building. This was generally divided into many small batches of differently processed powder which dried non-uniformly in difierent parts of the dry house, causing frequent ingress and egress to the dry-house by the operators, very definitely a hazard since each trip to the dryhouse by any operator created the possibility of accident. My invention makes it possible to do away with the prolonged, non-uniform drying of such large quantities of explosive in a single building.

It will be apparent to those skilled in the art that the mode of operation of the apparatus described above will lend itself readily for use with any type of powder from which the solvents are to be recovered and it will also be understood that variations in design and operation are contemplated and are within the spirit of this invention.

This application is a continuation-in-part of my application, Serial No. 325,515, filed March 23, 1940, which is in turn a division of my application, Serial No. 256,314, filed February 14, 1939.

What I claim and desire to protect by Letters Patent is:

1. A smokeless powder processing apparatus comprising a cylindrical tank, an opening having a gas-tight cover in the top of said tank adapted for charging smokeless powder grains into said tank, a distributing cone below said opening forming a distributing means to peripherally dispose said grains in said tank, a false bottom in said tank to support said grains, said bottom being foraminous, funnel shaped and having an angle of inclination of between about 25 and about 33 from the horizontal, a discharge valve at the vortex of said funnel shaped bottom for removing said grains from said tank, said discharge valve having an elongated and enlarged stem adapted to prevent said powder grains from covering said valve, conduit means connected to said tank above and below said false bottom, and means to circulate a gaseou medium through said tank connected in said conduit means.

2. A smokeless powder processing apparatus comprising an upright cylindrical tank, peripheral charging means in the top, and a central discharging means in the bottom thereof, said charging means adapted to fill said tank with powder grains and comprising an opening with a gas-tight cover and said discharging means adapted to remove said grains from said tank and 10 comprising a gas-tight valve, said gas-tight valve having an elongated and enlarged stem adapted 

